1. Field of the Invention
This invention generally relates to a linear motion guide unit, and, in particular, to such a linear motion guide unit including a retainer which retains rolling members in position and which is moved in synchronism with a bed and a table.
2. Description of the Prior Art
A linear motion rolling contact guide unit is well known in the art and it typically includes a bed, a table, a plurality of rolling members, such as balls or rollers, interposed between the bed and the table and a retainer for retaining the rolling members in position between the bed and the table. Also known is such a linear motion guide unit including a belt for preventing the retainer from being shifted in position as disclosed in the Japanese Patent Laid-open Pub. No. 56-113824. In this unit, however, since a pair of pulleys is disposed on both ends of the retainer and the top and bottom transfer surfaces are connected by belts via respective belts, whereby the movement of the retainer is limited to a half of the bearing unit or guide unit itself through the pulleys and belts and the belts also serve as dust covers.
However, in the prior art structure utilizing belts for preventing the retainer from shifting in position, since the pulleys are disposed outside of the bed and the table, the overall length of the bearing unit or guide unit tends to become excessively long. Besides, in the prior art device, since a pulley is provided at each end of the retainer, the total length of the retainer tends to be longer and the weight of each of these pulleys is added to the bearing unit or guide unit, so that the retainer is more susceptible to deformations and there is also a disadvantage of an increase in the partial abnormal wear and sliding resistance.